Hey Tim,
Thank you for reaching out to us! I’m very sorry about this issue you are experiencing. A few weeks ago we released the latest versions of The Events Calendar (TEC) and Events Calendar Pro (ECP) with a permalink update for recurring events (the permalink logic was removed from TEC and implemented on ECP instead). Please make sure both plugins are up to date.
If both plugins are up-to-date and the issue persists, please access your Dashboard and head over to Settings -> Permalinks for a permalink flush (no need to change anything, just visit the permalinks page: WordPress will automatically flush your permalinks once you visit it).
If you need anything else in the meantime, please let me know and I’ll be happy to assist!
Regards,
Patricia